Method of manufacturing permanent magnets having large coercive force



Aug. 31, 1965 HAKARU MAsUMoTo ETAL 3,203,838

METHOD OF MANUFACTURING PERMANENT MAGNETS HAVING LARGE COERCIVE FORCE Filed Sept. 24, 1963 2 Sheets-Sheet l Fig.|.

A lsoo O E.. leso E 2 looo Mognehc Trunsformuhon E 75 poln 0 soo D f- 25o o s lo l5 2o 25 Aluminium A Ni C0 l 2Ol 80 I F|g.2- Ni/, NifCoIZOBO so 4o o o 0 lo y 3\/ 2V un Residual inducfion (G 5o so 'ro b ao so coercive Force (Oe) HAA/A'Pu MASQ/wore TAKE@ A/oA YAs/-f/ K/ YosH/ WATA/vAE Aug. 31, 1965 HAKARU MAsUMoTo ETAL METHOD OF MANUFACTURING PERMANENT MAGNETS HAVING LARGE COERCIVE FORCE Filed Sept. 24, 1963 Hcio moo

Hc (0e) Mogneiic field (0o) Residual induction, B

2A Sheets-Sheet 2 United States Patent O 3,203,838 METHOD F MANUFACTURING PERMA- 'NENT MAGNETS HAVING LARGE CO- ERCIVE FORCE Hakaru Masumoto, Sendai, Takeo Kobayashi, Nator, and Kiyoshi 'Watanahe, Sendai, Japan, assignors to The Foundation: The Research Institute of Electric and Magnetic Alloys, Sendai, Japan, an incorporated foundation of Japan Filed Sept. 24, '1963, Ser. No. 311,003 'Claims priority, application `lapan, Sept. 28, 1962, 37/42,13'42 5 Claims. (Cl. 148-101) The present invention relates to a method of manufacturing permanent magnets having a large coercive force, more particularly, to permanent magnets consist ing essentially of about 20 to 92% of Co, 7.9 to 26% of Al and nickel in an effective amount up to about 65%.

The principal object of the invention is to obtain permanent magnets having large coercive force more easily and at a lower cost.

Heretofore known single domain particle magnets are compressed iron powder magnets, compressed Fe-Co powder magents, Bismanol (Mn-Bi alloys) and Ferroxdure (BaO.6Fe2O3), all of which have pretty large residual induction (Br) and coercive force (Hc), but in manufacturing such magnets it is necessary to prepare at irst very line, but suitable sized magnetic particles, then the powder should be compressed with an appropriate pressure and some of them should be sintered further at a higher temperature. More particularly, in the former two magnets it is very dicult to produce tine particles of a desired size and the method of its manufacture is pretty complicated, in other words, the above known magnets have disadvantages that the manufacture is generally very complicated and diiiicult and moreover, can not give always the product having the same characteristics.

In order to overcome the above described difficulties, the inventors have selected such alloys which precipitate single magnetic domain particle phase in the matrix of non-magnetic property by a simple heat treatment and tried to obtain single domain particle magnets having a large coercive force and found that Co-Al alloys containing l0 to 25% Al is adapted to the object of the invention and shows a very large coercive force such as 1,320 oersteds by subjecting to a proper treatment.

The inventors made further investigations by adding Ni to the Co-Al alloys and accomplished to nd out single domain particle magnets having much larger coercive force.

In carrying out the invention into effect, a colbaltaluminum-nickel ternary alloy consisting essentially of about 20 to 92% of cobalt, about 7.9 to 26% of aluminum and an effective amount up to about 65% of nickel, after casting in a metal or sand mold or the like to be quickly cooled or after heat treating at a temperature above the solid solubility line for a suitable time to produce a homogeneous solid solution structure and quenching in air, water or oil or other suitable fluid medium, is heated to a temperature above 350 C. for a suitable time, or when the alloy is cast in a mold, or when the alloy is plunged into a suitable medium after being subjected to said solid solution treatment, the cooling speed is properly reduced to precipitate ferromagnetic tine particles in the non-magnetic matrix, thereby providing permanent magnets having large coercive force.

The accompanying drawings illustrate curve diagrams showing the properties of the alloys of the invention, of which- FlG. 1 illustrates the sectional diagram of Ni:Co:20:80

ice

in the Co-Al-Ni ternary equilibrium diagram (a-b section in FIG. 2);

FIGS. 2(A) and (B) show equi-value curves statistically found from the measured magnetic values (black points illustrate the composition of the measured alloy);

FIG. 3 shows curves illustrating the relation between the magnetic property and the tempering temperature and time for alloys No. 10, No. 24 and No. 30 in the table, and

FIG. 4 shows the demagnetization curves of the alloys G, No. 21 and No. 30 in the table.

Now the results of investigations made by the inventors will be explained in detail.

At first, in order to manufacture the alloy of the invention a suitable amount of Co and Ni Was melted in air, inert gas or vacuum by using a suitable melting furnace, then a small amount of degassing agent such as Mn, Si, Al or Ti was added to eliminate gasses, then further a suitable amount of Al was added and thoroughly agitated, thereby obtained molten alloy having homogeneous structure, then the melt was poured into a mold of a suitable shape and size to provide a sound ingot or product. According to the composition the forgeable ingot was forged at a suitable high temperature to provide the product of a desired shape.

Next, the above casting or forging was heated at a suitable temperature higher than the solid solubility line c-d in FIG. l, thereby its greater part becomes e solid solution. Then they were heated at a suitable temperature lower than the c-d solid solubility line and Within the region of e-l-g to precipitate single magnetic domain particles ,of g' phase in a non-magnetic matrix of e. The product thus obtained, when it is magnetized in a strong magnetic field, showed a large coercive force such as 1,600 oersteds (Oe) at the maximum and provided the magnet having a greater coercive force than that of Co-Al binary alloy.

Referring to FIGS. 2(A) and (B) there are shown compositions of a number of alloys melted in air by black points and the curves are of equimagnetic value statistically obtained from the results measured about the magnetic properties of these alloys. The properties of the typical alloys (points of larger circles in FIG. 2) are shown in the following table:

Further, the following relation is obtained from FIGS. 2(A) and (B).

Co (percent) Al (percent) Ni (percent) Br( G) Hc (0e) 20 -92 7. 9-26 0-65 1, 000-4, 300 200-1, 600 36 -89 11 -24 0-49 1, 2006, 000 500-1, 600 37 -88 12 -22 0-48 l, 500-5, 800 8004, 600 39 -87 12. 5-20. 5 0-46 l, 800-5, 300 1, 000-1, 600 42 -86 13 -18 0-43 2, 20D-4, 500 1, 200-1, 600 44. 5-78 14 -17 7-40. 5 2, 50G-3, 400 1, 4001, 600

Accordingly, `Co-Al-Ni alloys of the invention may be classified into such alloys consisting of 20 to 92% Co, 7.9 to 26% Al, an effective amount up to 65 Ni; alloys consisting of 36 to 89% Co, 1l to 24% Al, an effective amount up to 49% Ni; alloys consisting of `37 to 88% Co, l2 to 22% Al, an effective amount up to 48% Ni;

valloys consisting of 39 to 87% Co, 12.5 to 20.6% Al,

an effective amount up to 46% Ni; alloys consisting of 42 to 86% Co, 13 to 18% Al, an effective amount up to 43% Ni; Ialloys consisting of 44.5 to `78% Co, 14 to 17% Al, `7 to 40.5% Ni, these alloys can develop the required magnetic properties by the heat treatment of the invention.

Composition (percent) Tempering treatment (BH) max. Mark of alloys Br (G) He (Oe) (X108) BrOe Remarks Co Al Ni C. Hr.

88.3 11. 7 0 500 2 5. 100 650 1. 19 Forgeable. 87. 8 12. 2 0 500 4 5, 700 800 2. 02 Do. a6. 4 13. e 0 55o 4 4, soo 1, 05o 2. 11 some-,what

forgeable. 85. 4 14. 6 0 550 4 4, 300 1. 320 2. 38 83. 4 16. 6 0 550 3 3, 800 1, 310 2. 02 Unlftrgea e. 80. 4 19. 6 0 500 16 2, 400 l, 200 1. O0 Do. 86. 7 10. 8 2. 5 560 1 4, 500 380 Forgeable. 84. 8 12. 6 2. 6 560` 3 5, 000 1, 200 1. 88 D0. 82.9 14. 5 2. 6 560 3 4, 000 1, 400 2. 20 Unrgea e. 79. 7 17. 8 2. 5 560 3 3, 000 1, 356 1. 15 D0. 7l. 5 23. 1 5. 4 570 3 l, 000 300 D0. 82.2 10. 8 7. 0 560 1 3, 500 350 78. 5 14. 3 7. 2 560 V3 3, 600 l, 420 1. 84 Untftrgea e. 79. 7 11. 0 9. 3 560 3 2. 700 300 78. 6 12. 4 9. 0 560 3 3, 800 1, 300 1. 55 Forgeable. 76. 4 14. 5 9. 1 560 3 3, 500 1, 500 1. 65 Somewhat forgeable. 75. U 15. 8 9. 2 560 3 3, 200 l, 580 1. 55 Unllgtrgea e. 69. 7 21. 2 9. 1 570 3 906 500 Do. 74. 2 14. 5 11. 3 560 3 3, 400 1, 500 1. 64 Somewhat forgeable. 76. 2 11. 8 12. 0 560 1 3, 400 580 Forgeable. 64. 7 22. 1 13. 2 570 3 600 500 Unrrgea e. 71. 1 14. 7 14. 2 560 3 3, 400 1, 500 1. 63 Forgeable. 69. 5 16. 4 14. 1 560 6 3, 000 1, 500 1. 50 Unlgfrgea e. 69. 0 14. 7 16. 3 560 3 2. 800 1, 580 1. 45 Forgeable. 67. 2 14. 6 18. 2 560 3 3, 600 1, 450 1. 64 Do. 67. 2 12.8 20. 0 560 3 3, 800 870 Do. 65. 1 14. 7 20. 2 560 3 3, 400 1. 550 1. 73 Unforgeable. 60. 0 20. 0 20. 0 570 3 700 500 Forgeable. 62. 1 15. 8 22. 1 560 3 2, 500 1, 600 1.42 Do. 65. 3 14. 5 22. 2 560 3 3, 300 1 62 65. 0 11. 8 23. 2 560 1 3, 000 300 69. 0 14. 7 26. 3 560 3 3, 000 57. 1 14. 7 28. 2 560 3 3, 000 53. 1 14. 6 32. 3 560 3 3, 100 49. 5 18. 3 32. 2 560 6 500 able. 50. 4 14. 5 35. 1 560 6 3, 060 1, 600 1. 55 Forgeable. 47. 2 l2. 8 40. 0 560 1 3, 000 400 D0. 41. 2 18. 7 40. 1 560 6 500 400 Ungrgea e. 44. 2 14. 8 41. 0 560 6 2, 700 1, 580 1. 30 Forgeable. 40. 2 14` 7 45. 1 560 3 2, 200 1, 300 0. 80 D0. 37. 5 17. 4 45. 1 560 6 700 500 Ungrgea e. 35. 0 20. 0 45. 0 570 6 0 0 Do. 39. 2 12. 7 48. 1 560 3 1, 400 Forgeable. 35. 3 14. 7 50. 0 560 3 l, 200 32. 2 17. 5 50. 3 560 6 500 29. 8 15. 2 55. 0 560 3 700 Next, FIG. 3 illustrates characteristic curves showing Ithe results of experiments about the change of magnetic properties according to the change of tempering temperyature and time after the solid solution treatment of the alloys No. 10, No. 24 and No. 30 having a large coercive force.

As apparent from the table and the curves, the values of Br and (BI-Umax. decrease by the addition of Ni to the Co-Al binary alloys but the coercive force increases to a substantial value, that is, it will be `apparent that according to the invention, a considerably large coercive force can be obta-ined by a simple method of manufacturing the alloy and heat treatment. In case of metal mold casting and water quenching in FIG. 3 the cooling speed is considerably large so thatne particles in g phase do not substantially precipitate and magnetic property is considerably inferior but if the cooling speed is properly reduced somewhat excellent properties can be obtained without further subjecting to the tempering.

FIG. 4 illustrates the demagnetization curves of .the alloys G, No. 21 and No. 30. As seen from .the table, when the content of Al is comparatively small, the alloy is forgeable, but as the content of Al increases, the forging becomes diicult and as Al increases further the forging becomes substantially impossible, and those alloys have pretty low specific gravity as they contain Al.

The reason why the Al content is limited to 7.9 to 26% in the invention'is due to the fact that when Al is less than 7.9% and increases more than 26% ythe alloy decreases the coercive force and the residual induction aS apparent `from FIGS. 2(A) and (B), so that Al was limited as defined.

Co was limited to 20 to 92% by the reason that at more than 92% and less than 20% the coercive force and residual ux are reduced.

The reason why the Ni content Was limited to 65% is based on the fact that at more .than 65 Ni the residual induction and coercive force `are reduced as shown in FIGS. A2;(A) and (B).

Y In short, in the method of the invention, the alloy consisting essentially of about 20 to 92% Co, 7.9 to 26% Al and an eiective amount up to 65 Ni and a small amount of impurities, after it is cast in a metal or sand mold or the like to be rapid-cooled, or after quenched from a high temperature above the solid solubility line by a suitable method to be made as solid solution, is tempered at a suitable temperature below the solid solubility line within the e+ binary region for a suitable period or When cast in a metal mold or sand mold, or When cooled to a room temperature from the temperature above the solid solution line, the cooling speed is suitably reduced to precipitate single domain particles of ferromagnetic properties in the non-magnetic matrix of e, thereby attaining to develop very high coercive force, such as 1,600 oersteds and the residual induction is substantially larger than that of the ferrite magnets, thus the invention has specialities and large advantages industrially since the method of the invention is most suitable for the production of specially short magnets and enabling forging by 5 the selection of composition and reducing the specific gravity.

What We claim is: 1. A method of manufacturing high coercive force permanent magnets, comprising heating an alloy consisting 5 essentially of about Ztl-92% cobalt, 7.9-26% aluminum, and an effective amount up to `about 65% nickel to a temperature above the e+ binary region, quenching the alloy to a temperature below the upper boundary of .the e-l-g binary region, heating the alloy -in said binary region at a temperature sucient to precipitate ne particles of ferromagnetic in a matrix of inonmagnetic e, and magnetizing the product thus obtained in a strong magnetic eld to obtain a permanent magnet having high coercive force.

2. A method as claimed in claim 1, in which said alloy 15 consists essentially of about 36-89% cobalt, l1-24% aluminum, and an effective amount up to about 49% nickel.

3. A method as claimed in claim 1, in which said alloy n 6 consists essentially of about 44.578% cobalt, 14-17% aluminum, and 7-40.5% nickel.

5. A method as claimed in `claim 1, in which said temperature is above about 350 C.

References Cited by the Examiner UNITED STATES PATENTS 2,082,041 `6/ 37 Williams 148-1-02 2,118,285 5/38 Zumbusch 148-102 2,245,477 6/41 Jonas 148-1101 2,442,762 t6/ 48 Ellis 148-102 2,664,874 1/54 Graham 75-170 FOREIGN PATENTS 370,630 4/ 32 Great Britain.

OTHER REFERENCES Schramm, I.: Article Z. Metallkunde, vol. 33, pages 403-412, December 19441.

DAVID L. RECK, Primary Examiner. 

1. A METHOD OF MANUFACTURING HIGH COERCIVE FORCE PERMANENT MAGNETS, COMPRISING HEATING AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 20-92% COBALT, 7.9-26% ALUMINUM, AND AN EFFECTIVE AMOUNT UP TO ABOUT 65% NICKEL TO A TEMPERATURE ABOVE THE E+$ BINARY REGION, QUENCHING THE ALLOY TO A TEMPERATURE BELOW THE UPPER BOUNDARY OF THE E+$ BINARY REGION, HEATING THE ALLOY IN SAID BINARY REGION AT A TEMPERATURE SUFFICIENT TO PRECIPITATE FINE PARTICLES OF FERRO/ MAGNETIC $ IN A MATRIX OF NONMAGNETIC E, AND MAGNETIZING THE PRODUCT THUS OBTAINED IN A STRONG MAGNETIC FIELD TO OBTAIN A PERMANENT MAGNET HAVING HIGH COERCIVE FORCE. 